The invention relates to an optoelectronic semiconductor device comprising a semiconductor body with a semiconductor substrate of a first conductivity type on which are at least present in that order a first cladding layer of the first conductivity type, an active layer, a second cladding layer of a second conductivity type, an intermediate layer, and a third cladding layer also of the second conductivity type, the thickness of the second cladding layer being such that the intermediate layer is within the optical field profile of the active layer, while the intermediate layer comprises a semiconductor material having a lower bandgap than the second and third cladding layers.
Such optoelectronic semiconductor devices are used inter alia as radiation guides, LEDs or diode lasers. In the case of diode lasers, they are mainly used as radiation sources for inter alia information-processing systems such as laser printers, with which information is written, optical disc systems such as Compact Disc (Video) (CD(V)) players or bar code readers, with which information is read, and Digital Optical Recording (DOR) systems, with which information is written and read. In addition, diode lasers are used as transmitters in systems for glass fibre communication.
Such a device in the form of a semiconductor diode laser is known from European Patent Application no. 90314466.5 which was published 4 Sep. 1991 under no. 0 444 366. This document describes a diode laser having a mesa or a groove structure in which on an n-Gas substrate an active InGaP layer, is present between two cladding layers of n- and p-InAlGaP, respectively, over which an intermediate layer, here a thin InGaP layer, is present on which a third cladding layer of p-InAlGaP is arranged. The intermediate layer which serves as an etching stopper layer lies within the amplification profile of the active layer.
A disadvantage of the known optoelectronic semiconductor device is that in practice no suitable thickness for the etching stopper layer is found: with a thinner intermediate layer (for example, 3 nm thickness) etching sometimes continues through this layer. This is true especially when the layer(s) to be selectively etched above the intermediate layer varies/vary in thickness over a slice, so that a somewhat longer etching time is required for ensuring complete removal of the said layer(s) everywhere on the slice. The intermediate layer is then exposed to the etchant for too long a period in those locations where the layer(s) to be selectively etched is/are thinnest. If the intermediate layer is somewhat thicker, for example approximately 10 nm, it is true that the intermediate layer functions well as an etching stopper layer, but it is found that the starting current of the diode laser is increased, which is undesirable.